Messing around with a dropper/hopper based T-FlipFlop powered by an observer. I was comparing two different designs: a hopperless version and this one I am posting about and needed a redstone lamp so I could see how many pulses the Observer was emitting. When I added the lamp the circuit went into oscillation. This should not happen and indicates something really wrong with the way redstone is being processed.

I have included two screen shots showing the version that works as expected (most of the time) and the one with the redstone lamp that enters oscillation.

Once built all that needs doing is to trigger the observer with a block update.

The droppers starting from the one powered by the observer are: Facing up, facing right into hopper. The dropper under the hopper is obviously facing the first dropper.

The comparator powers the sticky piston with a block attached.

Without the lamp attached placing a block under the observer causes one activation of the piston.

Attach the lamp as shown on the second image and place a block under the observer and note that the piston continually activates.